26 The Scaphoid: Nonunion with DISI–Volar Wedge Graft
▪ Rationale and Basic Science Pertinent to the Procedure
Even though scaphoid nonunions can initially be relatively asymptomatic, patients with nonunions are at risk to develop osteoarthritis with eventual pain and decrease range of motion.1 , 2 The flexion moment on the fractured distal fragment and resorption of the volar cortex over time results in the development of an apex dorsal angulation or “humpback deformity.” The humpback deformity is commonly associated with dorsal extension of the lunate ( Fig. 26.1A-D ). The carpal instability eventually leads to carpal collapse and arthrosis.1 , 2 Although correction of the scaphoid nonunion deformity will often correct the lunate extension, there will be some instances in which the lunate will be found to be “fixed” in extension and will require additional soft tissue mobilization ( Fig. 26.2 ). The goals of surgical treatment consist of realignment and repair of the scaphoid nonunion and correct the dorsal deformity of the lunate restoring more normal carpal kinematics are to restore carpal height and stability.3 , 4 , 5
The ideal candidate is the patient with a symptomatic nonunion and associated humpback deformity without advanced degenerative changes ( Fig. 26.3 ).
Patients with advanced degenerative changes [e.g., scaphoid nonunion advanced collapse (SNAC) wrist] should not undergo volar wedge graft because their symptoms may not improve after surgery. Patients with early degenerative changes around the distal radial styloid can still undergo volar wedge grafting with internal fixation, but a concomitant radial styloidectomy should be considered. Proximal pole nonunions are difficult to approach volarly and also do not create the typical humpback deformity caused by nonunions at the waist. Patients who smoke should be counseled on smoking cessation because it can potentially decrease the chance of healing. Nonunions of greater than 5 years’ duration have been shown to have a decreased rate of union.6 Avascular necrosis of the proximal pole is a relative contraindication.
▪ Surgical Technique
When considering the use of autogenous iliac crest graft, general anesthesia will be required. The patient is placed on the operating table in the supine position. A bump consisting of rolled blankets or sheets can be placed underneath the hip to help expose the prominence of the iliac crest. The surgical extremity is placed on a radiolucent table with the shoulder abducted to 90 degrees. A nonsterile tourniquet is placed on the upper arm of the surgical extremity. The surgical extremity and the ipsilateral iliac crest are then prepped and draped in the standard sterile fashion. The Esmarch bandage is used to exsanguinate the extremity, and the tourniquet is inflated.
A 5 cm long skin incision is marked along the course of the flexor carpi radialis (FCR) tendon in the distal forearm ( Fig. 26.4A-I ). At the level of the distal wrist crease, the skin incision is gently curved in a radial direction up to the level of the scaphotrapezial joint.
Once the skin is incised, care must be taken to protect the branches of the palmar cutaneous branch of the median nerve. The superficial communicating branch of the radial artery can be found crossing the surgical field distal to the wrist crease. This vessel must be ligated and divided. The FCR sheath is then incised along its radial border and retracted ulnarly, which helps protect the palmar cutaneous branch of the median nerve. A longitudinal incision is made through the floor of the FCR tendon sheath, extending through and preserving the radioscaphocapitate ligament. A longitudinal incision is then made along the volar capsule, starting at the distal pole of the scaphoid and extending proximally. Distraction of the thumb with ulnar deviation of the wrist can help expose the waist of the scaphoid. The nonunion site may be covered with fibrous tissue, making identification difficult. This may be facilitated by intraoperative fluoroscopy and by placing a 25 gauge needle into the nonunion site to level the proximal and distal fragments apart. A 0.045-in. or 0.062-in. Kirschner wire can be drilled into the proximal and distal fragments to serve as joysticks for manipulation. In order for the Kirschner wires not to interfere with the central placement of the compression screw, the proximal wire should be placed as proximal as possible, whereas the distal wire should be placed ulnarly. A high-speed burr or a small oscillating saw is then used to excise the sclerotic edges of the nonunion until healthy bleeding bone is encountered. Care must be taken not to disrupt the dorsal cortex, which carries the blood supply. Keeping the dorsal hinge intact also prevents complete destabilization of the two fragments, which makes correction of the humpback deformity easier. Cysts within the nonunion must be excavated using curettes.
The scaphoid is then reduced by manipulation of the Kirschner wire joysticks to extend the proximal and distal fragments while opening up the nonunion site. Restoration of the carpal alignment usually occurs after correction of the humpback deformity. The length, width, and depth of the nonunion site are measured. A trapezoidal bone graft is then harvested from the iliac crest. The final graft should be 2 mm oversized after it is trimmed. Additional cancellous bone is curetted from the iliac crest and packed into any cystic defects in the scaphoid. The nonunion site is distracted and the graft inserted into the nonunion with help of a bone tamp and mallet. The graft should be placed with the cancellous side facing the edges of the nonunion. Once the distraction is released, the bone graft should be stable. Fluoroscopy should then be used to check the carpal alignment and confirm the correction of the humpback deformity. Alternatively, the lunate can first be reduced from its extended position into neutral alignment and then be percutaneously pinned from the radius to the lunate. The iliac crest bone graft can then be placed into the defect and then pinned with a Kirschner wire, followed by screw placement.5 , 7
The scaphotrapezial joint capsule is now incised to expose the trapezium. A small portion of the trapezium can be removed with a rongeur to have better access to the central axis of the scaphoid. The guide wire is then placed down the central axis of the scaphoid by angling the wire 45 degrees to the sagittal and coronal plane of the longitudinal axis of the forearm under fluoroscopic control. The guide wire should be advanced up to the subchondral bone of the proximal pole. A second wire can be placed radial and parallel to the guide wire to serve as a derotational wire. A depth gauge is then inserted over the guide wire to determine the screw length. The screw hole is then drilled 2 mm short of the length of the guide wire. A headless compression screw is chosen that is 4 mm short of the measured length to prevent impingement on the scaphotrapezial joint and to prevent overshooting of the proximal pole. The volar wedge graft should be stabilized with external pressure while the screw is being inserted to ensure that the graft does not dislodge or rotate. Any graft prominence on the radial volar aspect can be trimmed to prevent impingement on the radial styloid. Once the screw position is satisfactory under anteroposterior (AP), pronated oblique, and lateral fluoroscopic views, the guide wire and Kirschner wires are removed. The volar wrist capsule and volar ligaments are then repaired with a nonabsorbable suture. The tourniquet is deflated and hemostasis achieved. The skin is repaired. The wrist and thumb are then immobilized in a short-arm thumb spica splint.
The patient is then seen in the office in 10 to 14 days for suture removal and placed into a short-arm thumb spica cast. The patient is followed at regular intervals with x-rays and the cast is removed in 4 to 6 weeks followed by range of motion exercises.